Wall-painting and ornamentation have been decorative practices since the earliest recorded histories. From the 1600s through to 1900, the paints used for decoration changed very little in respect to the material make-up of the painting products. Industrial advancement at the end of the 19th century combined with the global cultural changes of the 20th century, propelled material developments and changes in painting products. Up to 1900, the paint materials primarily used were: water-based paints/distempers, lime washes, oil-based paints, and varnishes. Towards the end of the 19th century, Europeans began to use silicate mineral paints. Today in addition to the historic paints, decorative painters also use synthetic paints and clay paints.
Chemistry is an important variable in historic restoration and conservation as it relates to determining the compatibility of historic and restorative materials. While it is often best practice to replace in kind, many modern advancements in paint have provided more sustainable, long-term solutions. During the early stages of a project, a historic paint investigation and paint microscopy evaluation will uncover the history of the paint layers. During this investigation, tests are often performed to determine compatible materials for repair. As an owner, a report of these findings is helpful in understanding the material make-up of the building as well as the process of restoration.
Example of microscopy paint sample from the Basilica of the Sacred Heart of Jesus
The following is a list of paints used in historic buildings and a brief description
1. Water-Based Paints
a. Whitewash: typically a mixture of white clay or white chalk with lime and water as a solvent.
b. Limewash: typically a mixture of water solvent, lime binder, and pigments for tinting.
c. Distemper: typically a mixture of water, glue binder (various types depending on application), and pigment.
d. Tempera: typically a mixture of water, egg binder (whole or parts depending on mixture necessary), and pigment. Sometimes vinegar is used as a preservative and/or alcohol to disperse, mix the pigments.
e. Casein: typically a mixture of water, milk protein binder, and pigments.
f. Acrylic: typically a mixture of pigments suspended in an emulsion consisting of acrylic resin and water. Compared to other water based paints, acrylics are more modern paints.
2. Oil-Based Paints
a. Linseed Oil: typically a mixture of linseed oil binder/solvent and pigment. Offers a durable, glossy finish.
b. Lead: typically a mixture of linseed oil binder/solvent and lead-based pigments.
c. Enamels: typically a mixture of oil-based paints with a resin varnish to achieve a harder, glossy finish.
3. Mineral-Based Paints
a. Silicate: typically a mixture of potassium silicate binders and pigment. The binder reacts with the substrate to create an inseparable bond.
Factors that may affect paint selection will include the desired sheen, durability needed, permeability of paint as it relates to substrate, historical precedent, and more. Selection of paints for new applications will depend on a variety of factors including substrate compatibility and long-term durability. Selection of materials for inpainting/conservation will also depend on preexisting finishes. Thinners and driers are used according to the needs dictated by the work and environment.
In regards to so many aspects of the historic restoration and conservation industry, we often encounter two polarizing ideologies in regards to “old” versus “new”. With such an extreme shift in design changes over the last 50-75 years, it is understandable why some are more inclined to the modern changes and others are not. However, both of these mentalities can hinder an objective analysis of what is most compatible and sustainable to the long-term stability of the building, interior, or artwork. “Old” does not equal better nor does “new”; objective analysis is crucial to determining compatible materials during paint selection.
